Concretes and mortars are cement compositions additionally containing aggregate (e.g., sand and rock) and water. When water is added to the cement, this forms a paste which then hardens to a solid structure. Various additives have been used in these cement compositions to modify their properties for specialized applications. Thus, long fibers such as asbestos reduce the sagging of these pastes and thus is beneficial when applying tiles to a vertical surface. Freezing point depressants are used when cements are to be poured in subfreezing temperatures. Cellulosic polymers have been used in cements to control sedimentation of particles in the pastes. Bentonite clay has been used for this purpose. Other polymers, such as the polyvinyl alcohols and methyl methacrylates, have been used to reduce friction when pumping these pastes and to otherwise modify their workability. Fumed silica is used as an additive to make stronger concrete with reduced permeability.